1. Technical Field
The invention generally relates to power distribution systems and communication networks. More particularly, the invention relates to a redundant and fault-tolerant combined power distribution system and communication network.
2. Background Description
A primary objective for any power distribution system or communication network is to minimize the likelihood of a loss of function in the event of a failure. While strategic routing and shielding of physically durable wiring can minimize the likelihood of a failure, fault tolerant systems are clearly advantageous if functionality is to be preserved when a failure (inevitably) occurs.
Power distribution systems and communication networks are subject to a wide variety of failure conditions, but primary among these are:                Break: a complete severing of the wire carrying the power or communications signal;        Full Short: a low-resistance, non-intermittent connection either to ground (in the case of a power distribution system) or to ground or between a differential pair (in the case of a communication network);        Partial Short: a relatively high-resistance or intermittent connection either to ground (in the case of a power distribution system) or to ground or between a differential pair (in the case of a communication network).        
In the case of a conventional power distribution system, a break results in a loss of power to all devices “downstream” of the cut. Similarly, a full short removes power from downstream devices, and may additionally damage devices with inadequate current overload protection. A partial short can cease device function, lead to erratic device function, or damage one or more devices.
The importance of addressing such failures is increasing with the more frequent deployment of higher voltage power distribution systems, such as the move from 12- to 42-volt vehicle power distribution systems. For example, a higher voltage system is much more likely to support an arc between exposed wiring and the vehicle chassis, creating a short to ground. Similarly, an increased hazard is presented by in-line arcs across severed wires which are carrying current.
In the case of a communications network, such as a conventional Controller Area Network (CAN-bus), a break separates the bus into two improperly terminated segments. Communication between devices on opposing sides of the cut is no longer possible. Reflection associated with the improper termination may even inhibit communication between devices within one segment. A full short, either to ground or between a differential pair, effectively pulls the logic values to zero, rendering all communication on the bus impossible. A partial short also renders communication problematic if not impossible, and may even result in the introduction of spurious data.